An epoxy composite resin composition has excellent electric performance and adhesive strength. Therefore, it has been used for various fields of electricity and electronics in the past. In a case where a sufficient thermal resistance properties can not be obtained even when using an epoxy resin alone or in mixture, a high thermal resistant cyanate-epoxy composite resin compositions comprised of mixing epoxy resin with cyanate ester resin are commonly used as sealing materials of semiconductors or used for moldings such as base board for electronic circuits etc.
However, liquid epoxy composite resin compositions used for sealing semiconductors comprised of, for example, cyanate ester, epoxy resin, inorganic filler and dihydrazide compound etc. (Patent document 1) had disadvantages in that curing agents against cyanate ester and epoxy resin may be sometimes required respectively, and also a high curing temperature or long curing time was required.
In addition, it is proposed that an amine type curing agent is used for the composite composition which contains cyanate ester and epoxy resin (Patent document 2). However, in this case, there was a disadvantage in that sufficient storage stability was not obtained (Patent document 2).
Furthermore, in a case of a thermosetting resin composition wherein a latent curing agent containing imidazole component is used for cyanate ester and epoxy resin, the amount of cyanate resin used should be limited to obtain sufficient stability (Patent document 3). Thus, a satisfactory thermosetting resin composition has not been obtained yet.